Section 2.0 - Loads

ID #1172

Section 2.6.1: In the definitions section of 2.6.1, a 50-year mean recurrence interval is specified for wind on ice loading. However, in 2.6.8 a limit state factor of 2.0 is used. Per ASCEC10.4.6 paragraph 2, this factor of 2 is for a 500-year mean recurrence interval, not a 50-year mean recurrence interval. Therefore, if we are to design for a 50-year interval we must use a factor of 1.0, not 2.0. Will TIA acknowledge this fact and allow our company to use a factor of less than 2.0?If not, please explain your reasoning for using this 500-year storm event factor. Also, if TIA is unwilling to change said equation, is it acceptable to ask the jurisdiction to wave this factor in favor of the 50-year factor of 1.0?

The TIA-222-G Standard is based on limit state design and it is necessary to convert 50-year recurrence ice loading to 500-year recurrence to establish the limit state condition. The ice maps are based on working loads (50-year) mean recurrence interval. The 2.0 limit state conversion factor based in the standard is intended to convert the ice working load to a limit state load. It would not be acceptable to apply a 1.0 factor to ice thickness. This would be analogous to using a 1.0 load factor for the extreme wind loading condition based on the 50-year recurrence extreme wind loading map.

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Last update: 2015-06-04 18:09
Author: Bryan Lanier
Revision: 1.0

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